Exterior doors on many homes and other buildings, as well as interior doors to hotel rooms and the like, are commonly fitted with an interior security chain which secures the door in a partially-closed position. A chain mount bracket is typically attached to the wall adjacent to the door to be secured and a slotted door bracket is attached to the interior surface of the door. One end of an elongated security chain is attached to the chain mount bracket. The other end of the security chain is fitted with a sliding chain pin which is inserted in the elongated slot of the door bracket. Accordingly, when it is locked in place, the security chain is designed to enable partial opening of the door while preventing or hindering an intruder from forcing the door completely open. The security chain is also designed to prevent or hinder an intruder from forcing the door open when the door is closed.
One of the limitations of conventional security chains is that a strong or determined intruder can successfully push or kick the door open when the security chain is locked in place. Therefore, a door security alarm which is adapted to be mounted on a door and activated by a security chain is needed to emit an alarm signal in the event that an intruder attempts to force the door open.